Handling quality of service in a communication system

ABSTRACT

A method of providing a selected Quality of Service for calls traversing an IP Multimedia Subsystem. A control-plane Home IP Multimedia Gateway is interposed between the IP Multimedia Subsystem and at least one non-SIP client, such that SIP signaling may be exchanged with a remote client on behalf of the at least one non-SIP client. The Home IP Multimedia Gateway identifies a Quality of Service type by reference to the SDP part of one or more SIP messages, and the call leg between the non-SIP client and a residential gateway is configured accordingly.

FIELD OF THE INVENTION

The present invention relates to the handling of Quality of Serviceissues in a communications network and is applicable in particular toensuring quality of service interoperability between two or morenetworks, one of which is an IP Multimedia Subsystem Core Network.

BACKGROUND TO THE INVENTION

IP Multimedia (IPMM) services provide a dynamic combination of voice,video, messaging, data, etc. within the same session. By growing thenumbers of basic applications and the media which it is possible tocombine, the number of services offered to the end users will grow, andthe inter-personal communication experience will be enriched. This willlead to a new generation of personalised, rich multimedia communicationservices, including so-called “combinational IP Multimedia” serviceswhich are considered in more detail below.

IP Multimedia Subsystem (IMS) is the technology defined by the ThirdGeneration Partnership Project (3GPP) to provide IP Multimedia servicesover 3G mobile communication networks (3GPP TS 23.228 and TS 24.229Release 5 and Release 6). IMS provides key features to enrich theend-user person-to-person communication experience through theintegration and interaction of services. IMS allows new richperson-to-person (client-to-client) as well as person-to-content(client-to-server) communications over an IP-based network. The IMSmakes use of the Session Initiation Protocol (SIP) to set up and controlcalls or sessions between user terminals (or user terminals and webservers). The Session Description Protocol (SDP), carried by SIPsignalling, is used to describe and negotiate the media components ofthe session. Others protocols are used for media transmission andcontrol, such as Real-time Transport Protocol and Real-time TransportControl Protocol (RTP/RTCP), Message Session Relay Protocol (MSRP),Hyper Text Transfer Protocol (HTTP).

IMS requires an access network which would typically be a 2G/3G GeneralPacket Radio Service (GPRS)/Packet Switched (PS) network, but whichmight be some other access network such as fixed broadband or WiFi. FIG.1 illustrates schematically how the IMS fits into the mobile networkarchitecture in the case of a GPRS/PS access network.

The TISPAN working group of the European Telecommunications StandardsInstitute (ETSI) is currently working on a proposal for the NextGeneration Network (NGN) for fixed networks based upon IMS. As part ofthis project, consideration will be given to a so-called Home IMSGateway (HIG) which will allow non-IMS terminals to access IMS services.It is expected that the HIG will find applications in the home and smalloffice environments where users might wish to access IMS services usinga number of non-IMS enabled terminals which may or may not be SIPterminals. Examples of non-IMS but SIP enabled terminals are SIPtelephones and PCs, whilst examples of non-IMS terminals which do nothave SIP functionality are legacy telephones including DECT telephonesand IP device with UPnP support. The HIG will include a SIP gateway inorder to handle interoperability issues (e.g. conversion between SIP andother signalling protocols required by user equipment). Of course,alternatives to the TISPAN HIG proposal may well emerge in the future.

SUMMARY OF THE INVENTION

The new IMS based advanced multimedia services will impose high demandson the Quality of Service (QoS) characteristics end-to-end, from theserver in the operator network all the way into and through the “home”network. There are no existing solutions for QoS interoperabilitybetween the home network with its possible wide variety of Internalprotocols and the IMS/SIP protocols that are used to setup up sessionsoutside the home network. In the absence of a solution, all applicationsrunning on different devices within the home network will have an equalopportunity to transmit data frames. Whilst this may be adequate fordata traffic associated with applications such as web browsers, filetransfers, or email, it is inadequate for multimedia applications. Inparticular, the quality of high speed and/or high demanding multimediaservices (such as HDTV, VoIP and videoconferencing) cannot beguaranteed.

According to a first aspect of the present invention there is provided amethod of ensuring an end-to-end Quality of Service for calls traversingan IP Multimedia Subsystem, the method comprising:

-   -   interposing a Home IP Multimedia Subsystem Gateway at the        control plane between the IP Multimedia Subsystem and at least        one non-SIP client;    -   at the Home IP Multimedia Subsystem Gateway, exchanging SIP        signalling with a remote client on behalf of said non-SIP        client, the Gateway performing a mapping between a media type        identified within the SDP part of one or more SIP messages and a        Quality of Service type specified for a protocol used to control        the Quality of Service in the call leg between the non-SIP        client and a Residential Gateway; and    -   configuring said call leg in accordance with the mapped Quality        of Service type.

In an embodiment of the invention, the method comprises selecting at theHome IP Multimedia Subsystem Gateway a mapping function appropriate forsaid protocol used to control the Quality of Service of a call legbetween the non-SIP client and the Residential Gateway, the mappingfunction being selected from a plurality of mapping functions.

The Residential Gateway may be, for example, a routed gateway or abridged gateway. The Residential Gateway may contain a UPnP InternetGateway Device.

By way of example, the protocol used to control the Quality of Serviceof a call leg between the non-SIP client and the Residential Gateway maybe one of; UPnP, WMM, and DiffServ.

Preferably, said step of configuring said call leg in accordance withthe mapped Quality of Service type comprises configuring at least theResidential Gateway (e.g. providing an Internet Gateway Device). TheHome IP Multimedia Subsystem Gateway may also configure one or more of;an Ethernet Switch, a WLAN Access Point, and IP Router. The protocolused to configure the Residential Gateway and entities in the call pathbetween the Residential Gateway and the non-SIP client, may be the sameprotocol used to control the Quality of Service at the non-SIP client.

Said step of configuring said call leg in accordance with the mappedQuality of Service type may comprise using said protocol to configure anode within the call path including the Residential Gateway. This nodemay be a node responsible for tagging packets or frames with a priorityvalue, for example an Internet Gateway Device, or it may be a noderesponsible for forwarding packets or frames based upon a priority valuecontained within the frame or packet.

According to a second aspect of the present invention there is provideda Home IP Multimedia Subsystem Gateway comprising:

-   -   a first interface for communicating with an IP Multimedia        Subsystem;    -   one or more second interfaces for communicating with client        terminals using a non-SIP call set-up protocol;    -   means for exchanging SIP signalling with a remote client on        behalf of a non-SIP client via said first interface, and for        performing a mapping between a media type identified within the        SDP part of one or more SIP messages and a Quality of Service        type specified for a protocol used over a second interface to        establish a call leg between the non-SIP client and a        Residential Gateway; and    -   means for configuring said call leg in accordance with the        mapped Quality of Service type.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a Home IMS Gateway within a homenetwork; and

FIG. 2 illustrates an event sequence for configuring Quality of Servicewithin a home network.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

As has already been mentioned above, it is proposed to introduce aso-called Home IMS Gateway (HIG) into the general IMS architecture. FIG.1 illustrates the HIG which is located in the home between the IMS andthe home network (at the control level). For SIP enabled terminals, theHIG acts as a Back-to-Back User Agent, whilst for non-SIP enabledterminals the HIG provides an interface between the IMS and non-IMSworld, translating between SIP and other protocols used in the homenetwork.

In order to address the issue of QoS interoperability between the homenetwork and the IMS, a new functionality is introduced into the HIG.From the perspective of QoS, this functionality allows the HIG to act asa traffic priority manager and QoS policyholder. It accesses the mediacapabilities of home devices and uses this information to negotiate QoSsession parameters per IMS traffic stream. Via a QoS Manager, the HIGcontrols various components of the home network, e.g. a WLAN AccessPoint, an Ethernet Switch, and a Residential Gateway as illustrated inFIG. 1.

For non-SIP enabled terminals, within any home network different clientsmay use different application layer protocols to communicate with theHIG (although it can be assumed that IP is used to handle addressing,routing, etc). However, one strong candidate for future convergence isthe UPnP (Universal Plug and Play) protocol. For the purpose of thefollowing discussion, it is assumed that UPnP is used by HIG to open upthe necessary ports in the residential gateway in order to acceptincoming media streams and sessions.

Considering further the example of FIG. 1, the client devices (only oneof which is illustrated) are assumed to also communicate with the HIGusing UPnP. It is also assumed that all clients use Ethernet as thephysical layer. During a call set up, the HIG initiates the QoS setupmechanism with the client. When a new session is being set-up, initiatedeither from the home network or from the outside world via the IMS, theHIG looks into the SDP part of SIP messages in order to understand whatQoS level is needed. HIG then initiates a UPnP QoS setup from itsinternal UPnP Control Point to negotiate and prepare the home networkpart of the media path for this new session.

Typically, an IMS call is initiated by the calling party sending a SIPINVITE message to the called party. The called party then returns a 200OK message, and the calling party acknowledges receipt of this, andcloses the setup phase, by sending an ACK message. Each of thesemessages will contain an SDP part, and the HIG must set the media typeof the SDP part in dependence upon the requirements and capabilities ofthe communicating parties, and configure the home network accordingly.

To establish a QoS path, the UPnP QoS Manager within the HIG requiresthe value of the TrafficClass variable as input along with the sourceand sink of the media stream. UPnP defines the following values of theTrafficClass variable: Network Control, Streaming Control, Voice, AV,Data, Audio, Images, Gaming, Other, and Background. The UPnP QoSframework [UPnP QoS architecture: 1.0, UPnP version 1.0, March 2005]specifies that the Control Point obtains the value of the TrafficClassfrom the stream source and this value is based on the media beingstreamed. The TrafficClass is passed to the UPnP QoS Manager [QoSManager description: 1.0, UPnP version 1.0, March 2005] which interactswith the UPnP QoS Policy Holder to get the TrafficImportanceNumber. UPnPspecifies the conversion of TrafficClass variable value to values ofTrafficImportanceNumber as shown in Table 1 below. UPnPTrafficImportanceNumber is mapped to IEEE 802.1p traffic type values asshown in Table 1. IEEE 802.1p is the protocol used to prioritiseEthernet traffic, specifying the traffic type values for inclusion inthe Ethernet frame headers. Layer 2 switches use the traffic type valuesto prioritise the forwarding of Ethernet frames.

Using the value of the TrafficImportanceNumber, the QoS Manager sets thelayer 2 packet tagging value for the respective stream in the clientacting as the source of the media. The QoS similarly sets the layer 2packet tagging value in the Internet Gateway Device (within theresidential gateway) so that incoming packets (from the IMS) areappropriately tagged. The QoS Manager also ensures that all intermediatedevices along the stream path have the resources to support the requiredQoS level of the media stream. The TrafficClass value is extracted bythe HIG parsing the SIP SDP exchanged between the home client and theIMS system. To establish a QoS path in the home network for the trafficstream of the home client, the HIG converts the SDP media type and itsattributes to the UPnP TrafficClass value.

FIG. 2 shows the event sequence between the HIG and a UPnP device withinthe home network. Upon intercepting the SIP SDP exchanged during callsession establishment, the HIG parses the message and extracts the mediadescriptor. As described in [RFC 2327, “SDP: Session DescriptionProtocol”], the SIP SDP includes the media announcements. An SDP mediasession is described as:

-   m=<media><port><transport><fmt list>

The media field contains a media type subfield with values: “audio”,“video”, “application”, “data” and “control”. The HIG maps the mediatype field to UPnP TrafficClass variable as shown in Table 2 below.

The UPnP QoS mechanism allows for a more precise definition of the mediastream than does SDP. This is reflected in the dual values to which someSDP media types can be mapped. Which traffic class variable an SDP mediatype is assigned to depends upon how sensitive a given media stream isto time delays. For example, audio streams requiring delays of less than10 ms will be mapped to TrafficClass ‘voice’, while streams with delaysless that 100 ms are mapped to TrafficClass ‘audio’. For the SDP mediatype ‘application’, interactive/real-time applications which are verydelay sensitive (such as games) will be mapped to the ‘gaming’TrafficClass, while non-interactive applications which are not sodelay-sensitive are mapped to the ‘data’ TrafficClass. As will beapparent from Table 1, both network control and streaming controlTrafficClasses are treated equally in terms of QoS, so the SDP mediatype ‘control’ can be mapped to either.

After the determination of the TrafficClass variable for an SDP mediatype, the Control Point in the HIG initiates the UPnP QoS setup. TheUPnP QoS setup involves a series of messages exchanged between the QoSManager and the source device, as well as with intermediate devices (allrepresented as UPnP devices in FIG. 1). At the end of the QoS setup, atleast the source client and IGD are set to tag media stream packets withthe layer 2 priority value corresponding to the TrafficImportanceNumber.

If parameterised QoS strategy is supported by UPnP as well as the mediatype, the HIG also extracts from the SIP SDP the bandwidth requirementfor the media stream and passes this value to the QoS Manager foradmission control as specified in section 7 of [QoS Manager description:1.0, UPnP version 1.0, March 2005].

The CableHome [CableHome 1.1 Specification, version 1.1, August 2005]architecture, which enables the delivery of new cable-based services todevices within the home, relies on UPnP for its QoS mechanism. Thereforethe mapping provided in table 2 is relevant for CableHome 1.1 QoS.

As already noted above, clients within the home network may useprotocols other than UPnP to communicate with the HIG. Examples are asfollows:

Wi-Fi Multimedia

To meet the need for QoS wireless networks, the Wi-Fi Alliance proposedWMM (Wi-Fi Multimedia) as a profile of the upcoming IEEE 802.11e QoSextensions for 802.11 networks. WMM prioritises traffic demands fromdifferent applications and extends Wi-Fi's high quality end-userexperience from data connectivity to voice, music, and videoapplications under a wide variety of environment and traffic conditions.WMM defines four access categories that are used to prioritise trafficso that these applications have access to the necessary networkresources. A mapping between these categories and those of SDP arepresented in Table 4 below.

Generic IEEE 802.1p Based Protocol

The HIG QoS mapping functionality also covers the scenario where ageneric protocol is used to set the IEEE 802.1p priority values in homedevices. In this case, HIG acts as an intermediary between the IMSsystem and the home QoS management system. In a home network environmentthat supports traffic prioritisation based on the IEEE 802.1p standard,the mapping from SDP is carried out according to Table 5 below

Non-UPnP home clients that support 802.1p are configured to tag packetswith the relevant p-bits out of band with respect to UPnP. The HIGpasses the p-bit value to the QoS mechanism which then sets the relevanttraffic priority level.

DiffServ

In a scenario where the home network QoS is based on DiffServ, the HIGcan act as an intermediary device for QoS translation for the trafficstreams related to the IMS system. Table 6 illustrates the mapping tablebetween SDP media types and DSCP (Differentiated Service Code Point).There are no standard mappings of DSCP to 802.1p; rather this is usuallya vendor solution. The relation in Table 6 is a possible mappingsolution.

A possible scenario is that several protocols may be used simultaneouslywithin the home network, e.g. UPnP and WMM. In this case, the HIG mustbe configured to interface both UPnP and WMM to the IMS network. Moreparticularly, the HIG must map between IMS QoS media types and those ofthe used home network protocols.

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above described embodiments withoutdeparting from the scope of the present invention. For example, theclient device itself may not support Quality of Service functionality.In this case, and with reference to FIG. 1, the UPnP device service isnot present within the client, and it is the WLAN Access Point (in thisexample) which sets the Level 2 priority tag in the Ethernet frameheader.

TABLE 1 UPnP IEEE 802.1p UPnP TrafficClass TrafficImportanceNumbertraffic type Network control 7 NC Streaming control 7 NC Voice 6 VOGaming 6 VO AV 5 VI Audio 5 VI Images 3 EE Data 0 BE Other 0 BE

TABLE 2 SDP UPnP TrafficClass Audio Voice/Audio Video Av ApplicationData/Gaming Data Data Control Network/Streaming control

TABLE 3 SDP bandwidth description UPnP bandwidth description b = rowTSpec: Mean data rate

TABLE 4 SDP WMM Audio Voice Video Video Application Best effort DataBackground

TABLE 5 SIP SDP 802.1p Control 7 Audio 6 Video 5 Application 3 Data 0

TABLE 6 SIP SDP DSCP DiffServ Profile Control 56 Control Audio 46Expedited forwarding Video 40 Express forwarding Application 26 AF31Data 0 Best effort

1. A method of ensuring an end-to-end Quality of Service for callstraversing an Internet Protocol (IP) Multimedia Subsystem, the methodcomprising: interposing a Home IP Multimedia Subsystem Gateway at acontrol plane between the IP Multimedia Subsystem and at least onenon-Session Initiation Protocol (non-SIP) client; mapping, by the HomeIP Multimedia Subsystem Gateway, between a media type identified withina Session Description Protocol (SDP) part of one or more SIP messagesexchanged via the Home IP Multimedia Subsystem Gateway and a Quality ofService type specified for a protocol used to control the Quality ofService in a call leg between the non-SIP client and a ResidentialGateway; and configuring said call leg in accordance with the mappedQuality of Service type.
 2. The method according to claim 1, furthercomprising selecting at the Home IP Multimedia Subsystem Gateway amapping function appropriate for said protocol used to control theQuality of Service of a call leg between the non-SIP client and theResidential Gateway, the mapping function being selected from aplurality of mapping functions.
 3. The method according to claim 1,wherein said Residential Gateway is a routed gateway.
 4. The methodaccording to claim 1, wherein said Residential Gateway contains aUniversal Plug and Play (UPnP) Internet Gateway Device.
 5. The methodaccording to claim 1, wherein the protocol used to control the Qualityof Service of a call leg between the non-SIP client and the ResidentialGateway is one of Universal Pluq and Play (UPnP), Wi-Fi Multimedia(WMM), and Differentiated Services (DiffServ).
 6. The method accordingto claim 1, wherein said step of configuring said call leg in accordancewith the mapped Quality of Service type comprises configuring at leastthe Residential Gateway.
 7. The method according to claim 6, whereinsaid step of configuring said call leg further comprises configuring oneor more of an Ethernet Switch, a Wireless Local Area Network (WLAN)Access Point, and an IP Router.
 8. A Home Internet Protocol (IP)Multimedia Subsystem Gateway comprising: a first interface forcommunicating with an IP Multimedia Subsystem; at least one secondinterface for communicating with client terminals using a non-SessionInitiation Protocol (non-SIP) call set-up protocol; means for exchangingSIP signaling with a remote client on behalf of a non-SIP client viasaid first interface, and for performing a mapping between a media typeidentified within a Session Description Protocol (SDP) part of one ormore SIP messages and a Quality of Service type specified for a protocolused over a second interface to establish a call leg between the non-SIPclient and a Residential Gateway; and means for configuring said callleg in accordance with the mapped Quality of Service type.
 9. The HomeIP Multimedia Subsystem Gateway according to claim 8, further comprisingmeans for selecting at the Home IP Multimedia Subsystem Gateway amapping function appropriate for said protocol used to control theQuality of Service of a call leg between the non-SIP client and theResidential Gateway, the mapping function being selected from aplurality of mapping functions.
 10. The method according to claim 1,wherein said Residential Gateway is a bridged gateway.